Returning to a prior week's study of my Canon f/2.8 70 to 200 mm L lens, I put it through its paces at a Padres vs. Colorado Rockies game. The gallery of baseball shots ** can be found at this location. **
Of interest is that the first 8 are taken with the “L” lens. And in a few cases I used my 2x extneder also. For further comparison, note that the rest were taken earlier in the year with my trusty Canon EF 75-300mm f/4-5.6 USM zoom.

I found the 2x extender to be almost too much for this setting. For one thing I accidently cracked the guy in front of me on the head with the extended lens and hood. Also it got me too close to the action sometimes. I was shooting RAW at 240 dpi which enabled me to get my best shots at a mere 200mm w/o the extender. I was using a monopod on all shots.